1. Statement of the Technical Field
The inventive arrangements relate generally to methods and apparatus for providing increased design flexibility for RF circuits, and more particularly for optimization of dielectric circuit board materials for improved performance in transmission lines.
2. Description of the Related Art
RF circuits are typically formed in one of three ways. One configuration known as microstrip places a transmission line on a board surface and provides a second conductive layer, commonly referred to as a ground plane. A second type of configuration known as buried microstrip is similar except that the transmission line is covered with a dielectric substrate material. In a third configuration known as stripline, the transmission line is sandwiched in dielectric between two electrically conductive (ground) planes.
In conventional RF designs, transmission lines often have discontinuities, such as angles, bends, terminations and junctions. Notably, the discontinuities can cause undesirable affects such as ringing and reflection of RF signals conducted through the lines, resulting in voltage and impedance variations in the circuit. These voltage and impedance variations often degrade the RF signals, contribute to circuit resonances and increase electromagnetic interference (EMI) generated by the circuit. This can be especially of concern at RF frequencies above 1 GHz.
Circuit designers often attempt to minimize signal reflection and ringing by minimizing the usage of 90xc2x0 angles, sharp bends, and vias in a circuit. One technique commonly used is to make the bend radius of transmission lines relatively large, roughly three times the width of the transmission line. Another technique is to chamfer sharp angles in transmission lines. Nonetheless, these techniques generally are only moderately effective at controlling signal degradation, circuit resonances, and EMI.
The present invention relates to a circuit for processing radio frequency signals. The circuit includes a substrate board that has at least one dielectric layer having a first set of substrate properties over a first region and a second set of substrate properties over a second region. The substrate properties can include a permittivity and a permeability. The substrate properties of the second region can be different that the substrate properties of the first region. The substrate can comprise a meta-material and can be differentially modified to vary at least one of the permittivity and the permeability over a selected region.
The circuit also can include at least a first transmission line coupled to the substrate, the transmission line having at least one discontinuity. The discontinuity can include a bend, corner, via, non-uniformity, or transition in the first transmission line. The discontinuity also can include a junction between the first transmission line and a second transmission line or a transition/interconnect to a discrete circuit component. In one embodiment a transition element can be provided at the junction.
The discontinuity can be coupled to the second substrate region to reduce an amount of signal distortion and ringing caused by the discontinuity. The second region can be structured to be a column shape with a triangular or oval cross section. In another embodiment the second region can be in the shape of a cylinder.